Downlink wireless transmission schemes with inter-cell interference mitigation

ABSTRACT

A system and method for inter-cell interference avoidance. A device capable of performing channel estimation is configured to divide a codebook into two sets. A first set of said two sets corresponds to codebook information that will cause an interference in a received signal to be less than a threshold. The device further is configured to send feedback information corresponding to the first or second set, or both. A base station is configured to select a preceding vector or matrix based, in part, on a portion of the feedback information.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application is related to U.S. Provisional Patent No.61/133,094, filed Jun. 25, 2008, entitled “INTERCELL INTERFERENCEAVOIDANCE FOR DOWNLINK TRANSMISSION”, U.S. Provisional Patent No.61/133,846, filed Jul. 3, 2008, entitled “INTER-CELL INTERFERENCEAVOIDANCE FOR DOWNLINK TRANSMISSION” and U.S. Non-provisional Patentapplication Ser. No. 12/445,531, entitled “INTERCELL INTERFERENCEAVOIDANCE FOR DOWNLINK TRANSMISSION” filed concurrently herewith.Provisional Patent Nos. 61/133,094 and 61/133,846 are assigned to theassignee of the present application and are hereby incorporated byreference into the present application as if fully set forth herein. Thepresent application hereby claims priority under 35 U.S.C. §119(e) toU.S. Provisional Patent Nos. 61/133,094 and 61/133,846.

TECHNICAL FIELD OF THE INVENTION

The present application relates generally to wireless communicationnetworks and, more specifically, to an interference avoidance ofedge-cells in a wireless communications network.

BACKGROUND OF THE INVENTION

In a wireless communications network, multiple base stations (alsoreferred to as “eNBs”) use a standardized codebook for precodingtransmission to their respective user equipments (UEs), using multipletransmit antennas. A typical problem of this procedure occurs whereseveral base stations are serving their intended UEs while interferingwith each other's signal. This scenario is called “inter-cellinterference.” Inter-cell interference constrains the throughput of thewireless network.

FIG. 1B illustrates an exemplary wireless network 100. In such example,base station (BS) 102 is the serving base station for subscriber station(SS) 116, e.g., communications to and from SS 116 are conducted throughBS 102. BS 103 is the serving base station for SS 115, e.g.,communications to and from SS 115 are conducted through BS 103. SS 116is located in proximity to SS 115. Further, BS 102 is communicating withSS 116 using the same frequency band that BS 103 is using to communicatewith SS 115. Therefore, SS 116 receives communications 140 from BS 102.However, SS 116 also receives communications 145 (e.g., interferingcommunications) from BS 103. Further, SS 115 receives communications 150from BS 103. Additionally, SS 115 also receives communications 155(e.g., interfering communications) from BS 102. Since SS 116 and SS 115are in close proximity and using the same frequency band simultaneously,the communications between the subscriber stations, SS 116 and SS 115,and their respective base stations, BS 102 and BS 103, interfere witheach other.

SUMMARY OF THE INVENTION

A device capable of performing channel estimation is provided. Thedevice includes a processor; a memory; and a codebook partitioner. Thecodebook partitioner is configured to divide a codebook into two sets. Afirst set of said two sets corresponds to codebook information that willcause an interference in a received signal to be less than a threshold.Additionally, the processor is configured to send at least one of thetwo sets to a base station.

A wireless communications network is provided. The wirelesscommunications network comprises a plurality of base stations, each oneof the base stations is capable of selecting one of a plurality ofcodebooks for precoding. At least one of the base stations includes areceiver capable of receiving feedback information from at least onesubscriber station. The feedback information includes at least one of arecommended set of codebook information and a restricted set of codebookinformation. The controller identifies either the recommended set ofcodebook information or restricted codebook information.

A method for interference avoidance is provided. The method includesestimating channel information. The method also includes identifyingcodebook information that will cause an interference in a receivedsignal to be less than a threshold. Further, the method includesdividing a codebook into subsets, wherein at least one subsetcorresponds to the identified codebook information. Then, the methodincludes transmitting feedback information associated to the subset.

A method for interference avoidance is provided. The method includesreceiving feedback information. The feedback information includes a setof codebook information that identifies a recommended set or arestricted set. A response to the feedback information is determined. Apreceding matrix is selected based on the response.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1A illustrates exemplary wireless network 100 that is capable ofdecoding data streams according to an exemplary embodiment of thedisclosure;

FIG. 1B illustrates exemplary wireless network 100 according toembodiments of the present disclosure;

FIG. 2 illustrates a MIMO system 200 that is capable of decoding datastreams according to an embodiment of the present disclosure;

FIG. 3 illustrates details of multi-codeword MIMO encoder according toan embodiment of the present disclosure;

FIG. 4 illustrates wireless subscriber station according to embodimentsof the present disclosure;

FIGS. 5A and 5B illustrate a codebook partitioner 470 according toembodiments of the present disclosure;

FIG. 6 illustrates a time diagram for interference avoidance accordingto embodiments of the present disclosure;

FIG. 7 illustrates a process for interference avoidance according toembodiments of the present disclosure;

FIG. 8 illustrates another process for interference avoidance accordingto embodiments of the present disclosure;

FIG. 9 illustrates a process for codebook selection according toembodiments of the present disclosure; and

FIG. 10 illustrates another process for interference avoidance accordingto embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 10, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless communication network.

With regard to the following description, it is noted that the LTE term“node B” is another term for “base station” used below. Further, theterm “cell” is a logic concept which can represent a “base station” or a“sector” belongs to a “base station”. In this patent, “cell” and “basestation” are used interchangeably to indicate the actual transmissionunits (may be “sector” or “base station” etc.) in the wireless system.Also, the LTE term “user equipment” or “UE” is another term for“subscriber station” used below.

FIG. 1A illustrates exemplary wireless network 100 that is capable ofdecoding data streams according to one embodiment of the presentdisclosure. In the illustrated embodiment, wireless network 100 includesbase station (BS) 101, base station (BS) 102, and base station (BS) 103.Base station 101 communicates with base station 102 and base station103. Base station 101 also communicates with Internet protocol (IP)network 130, such as the Internet, a proprietary IP network, or otherdata network.

Base station 102 provides wireless broadband access to network 130, viabase station 101, to a first plurality of subscriber stations withincoverage area 120 of base station 102. The first plurality of subscriberstations includes subscriber station (SS) 111, subscriber station (SS)112, subscriber station (SS) 113, subscriber station (SS) 114,subscriber station (SS) 115 and subscriber station (SS) 116. Subscriberstation (SS) may be any wireless communication device, such as, but notlimited to, a mobile phone, mobile PDA and any mobile station (MS). Inan exemplary embodiment, SS 111 may be located in a small business (SB),SS 112 may be located in an enterprise (E), SS 113 may be located in aWiFi hotspot (HS), SS 114 may be located in a residence, SS 115 may be amobile (M) device, and SS 116 may be a mobile (M) device.

Base station 103 provides wireless broadband access to network 130, viabase station 101, to a second plurality of subscriber stations withincoverage area 125 of base station 103. The second plurality ofsubscriber stations includes subscriber station 115 and subscriberstation 116. In alternate embodiments, base stations 102 and 103 may beconnected directly to the Internet by means of a wired broadbandconnection, such as an optical fiber, DSL, cable or T1/E1 line, ratherthan indirectly through base station 101.

In other embodiments, base station 101 may be in communication witheither fewer or more base stations. Furthermore, while only sixsubscriber stations are shown in FIG. 1A, it is understood that wirelessnetwork 100 may provide wireless broadband access to more than sixsubscriber stations. It is noted that subscriber station 115 andsubscriber station 116 are on the edge of both coverage area 120 andcoverage area 125. Subscriber station 115 and subscriber station 116each communicate with both base station 102 and base station 103 and maybe said to be cell-edge devices interfering with each other. Forexample, the communications between BS 102 and SS 116 may be interferingwith the communications between BS 103 and SS 115. Additionally, thecommunications between BS 103 and SS 115 may be interfering with thecommunications between BS 102 and SS 116.

In an exemplary embodiment, base stations 101-103 may communicate witheach other and with subscriber stations 111-116 using an IEEE-802.16wireless metropolitan area network standard, such as, for example, anIEEE-802.16e standard. In another embodiment, however, a differentwireless protocol may be employed, such as, for example, a HIPERMANwireless metropolitan area network standard. Base station 101 maycommunicate through direct line-of-sight or non-line-of-sight with basestation 102 and base station 103, depending on the technology used forthe wireless backhaul. Base station 102 and base station 103 may eachcommunicate through non-line-of-sight with subscriber stations 111-116using OFDM and/or OFDMA techniques.

Base station 102 may provide a T1 level service to subscriber station112 associated with the enterprise and a fractional T1 level service tosubscriber station 111 associated with the small business. Base station102 may provide wireless backhaul for subscriber station 113 associatedwith the WiFi hotspot, which may be located in an airport, cafe, hotel,or college campus. Base station 102 may provide digital subscriber line(DSL) level service to subscriber stations 114, 115 and 116.

Subscriber stations 111-116 may use the broadband access to network 130to access voice, data, video, video teleconferencing, and/or otherbroadband services. In an exemplary embodiment, one or more ofsubscriber stations 111-116 may be associated with an access point (AP)of a WiFi WLAN. Subscriber station 116 may be any of a number of mobiledevices, including a wireless-enabled laptop computer, personal dataassistant, notebook, handheld device, or other wireless-enabled device.Subscriber station 114 may be, for example, a wireless-enabled personalcomputer, a laptop computer, a gateway, or another device.

Dotted lines show the approximate extents of coverage areas 120 and 125,which are shown as approximately circular for the purposes ofillustration and explanation only. It should be clearly understood thatthe coverage areas associated with base stations, for example, coverageareas 120 and 125, may have other shapes, including irregular shapes,depending upon the configuration of the base stations and variations inthe radio environment associated with natural and man-made obstructions.

Also, the coverage areas associated with base stations are not constantover time and may be dynamic (expanding or contracting or changingshape) based on changing transmission power levels of the base stationand/or the subscriber stations, weather conditions, and other factors.In an embodiment, the radius of the coverage areas of the base stations,for example, coverage areas 120 and 125 of base stations 102 and 103,may extend in the range from less than 2 kilometers to about fiftykilometers from the base stations.

As is well known in the art, a base station, such as base station 101,102, or 103, may employ directional antennas to support a plurality ofsectors within the coverage area. In FIG. 1, base stations 102 and 103are depicted approximately in the center of coverage areas 120 and 125,respectively. In other embodiments, the use of directional antennas maylocate the base station near the edge of the coverage area, for example,at the point of a cone-shaped or pear-shaped coverage area.

The connection to network 130 from base station 101 may comprise abroadband connection, for example, a fiber optic line, to serverslocated in a central office or another operating companypoint-of-presence. The servers may provide communication to an Internetgateway for internet protocol-based communications and to a publicswitched telephone network gateway for voice-based communications. Inthe case of voice-based communications in the form of voice-over-IP(VoIP), the traffic may be forwarded directly to the Internet gatewayinstead of the PSTN gateway. The servers, Internet gateway, and publicswitched telephone network gateway are not shown in FIG. 1A. In anotherembodiment, the connection to network 130 may be provided by differentnetwork nodes and equipment.

In accordance with an embodiment of the present disclosure, one or moreof base stations 101-103 and/or one or more of subscriber stations111-116 comprises a receiver that is operable to decode a plurality ofdata streams received as a combined data stream from a plurality oftransmit antennas using an MMSE-SIC algorithm. As described in moredetail below, the receiver is operable to determine a decoding order forthe data streams based on a decoding prediction metric for each datastream that is calculated based on a strength-related characteristic ofthe data stream. Thus, in general, the receiver is able to decode thestrongest data stream first, followed by the next strongest data stream,and so on. As a result, the decoding performance of the receiver isimproved as compared to a receiver that decodes streams in a random orpre-determined order without being as complex as a receiver thatsearches all possible decoding orders to find the optimum order.

FIG. 2 illustrates a MIMO system 200 that is capable of decoding datastreams according to an embodiment of the present disclosure. MIMOsystem 200 comprises a transmitter 205 and a receiver 210 that areoperable to communicate over a wireless interface 215.

Transmitter 205 comprises a multi-codeword MIMO encoder 220 and aplurality of antennas 225, each of which is operable to transmit adifferent data stream 230 generated by encoder 220. Receiver 210comprises a spatial processing block 250 and a plurality of antennas255, each of which is operable to receive a combined data stream 260from a plurality of sources including antennas 225 of transmitter 205.Spatial processing block 250 is operable to decode the combined datastream 260 into data streams 265, which are substantially identical tothe data streams 230 transmitted by antennas 225.

Spatial processing block 250 is operable to decode data streams 265 fromthe combined data stream 260 using an MMSE-SIC procedure that selects anorder for decoding the streams 265 based on a decoding prediction metric(DPM) for each stream 265. The DPM for each data stream 265 is based ona strength-related characteristic associated with the data stream 265.Thus, for example, the DPM may be based on a capacity of the channelassociated with the data stream 265, an effective signal-to-interferenceand noise ratio (SINR) for the data stream 265 and/or any other suitablestrength-related characteristic. Using this process for decoding,receiver 210 is able to provide better performance than a receiver thatdecodes streams in a random order without introducing the complexity ofa receiver that searches all possible decoding orders to find an optimumdecoding order.

FIG. 3 illustrates details of multi-codeword MIMO encoder 220 accordingto an embodiment of the present disclosure. For this embodiment, encoder220 comprises a demultiplexer (demux) 305, a plurality of cyclicredundancy code (CRC) blocks 310, a plurality of coders 315, a pluralityof modulators 320, and a pre-coder 325. Encoder 220 is operable toreceive an information block and to generate data streams 230 based onthe information block for transmission over antennas 225. Although theillustrated embodiment shows two sets of components 310, 315 and 320 togenerate two streams 230 a-b for transmission by two antennas 225 a b,it will be understood that encoder 220 may comprise any suitable numberof component sets 310, 315, 320 and 325 based on any suitable number ofstreams 230 to be generated.

Demultiplexer 305 is operable to demultiplex the information block intoa plurality of smaller information blocks, or streams 340. Each CRCblock 310 is operable to add CRC data to the associated stream 340.Following the addition of CRC data, each coder 315 is operable to codethe stream 340 and each modulator 320 is operable to modulate the codedstream 340. After coding and modulation, the resulting streams, whichare equivalent to data streams 230, are processed through a precodingalgorithm 325 and transmitted from separate antennas 225.

Because encoder 220 is a multi-codeword MIMO encoder, differentmodulation and coding may be used on each of the individual streams 340.Thus, for example, coder 315 a may perform different coding from coder315 b and modulator 320 a may perform different modulation frommodulator 320 b. Using multi-codeword transmission, a CRC check mayoptionally be performed on each of the codewords before the codeword iscanceled form the overall signal at receiver 210. When this check isperformed, interference propagation may be avoided in the cancellationprocess by ensuring that only correctly received codewords are canceled.

Precoding 325 is used for multi-layer beamforming in order to maximizethe throughput performance of a multiple receive antenna system. Themultiple streams of the signals are emitted from the transmit antennaswith independent and appropriate weighting per each antenna such thatthe link through-put is maximized at the receiver output. Precodingalgorithms for multi-codeword MIMO can be sub-divided into linear andnonlinear precoding types. Linear preceding approaches can achievereasonable throughput performance with lower complexity relateved tononlinear preceding approaches. Linear preceding includes unitarypreceding and zero-forcing (hereinafter “ZF”) precoding. Nonlinearpreceding can achieve near optimal capacity at the expense ofcomplexity. Nonlinear precoding is designed based on the concept ofDirty paper coding (hereinafter “DPC”) which shows that any knowninterference at the transmitter can be subtracted without the penalty ofradio resources if the optimal preceding scheme can be applied on thetransmit signal.

FIG. 4 illustrates wireless subscriber station 116 according toembodiments of the present disclosure. The embodiment of wirelesssubscriber station 116 illustrated in FIG. 4 is for illustration only.Other embodiments of the wireless subscriber station 116 could be usedwithout departing from the scope of this disclosure.

Wireless subscriber station 116 comprises antenna 405, radio frequency(RF) transceiver 410, transmit (TX) processing circuitry 415, microphone420, and receive (RX) processing circuitry 425. SS 116 also comprisesspeaker 430, main processor 440, input/output (I/O) interface (IF) 345,keypad 450, display 455, memory 460 and a codebook partitioner 470.Memory 460 further comprises basic operating system (OS) program 461 andthreshold ε 462.

Radio frequency (RF) transceiver 410 receives from antenna 405 anincoming RF signal transmitted by a base station of wireless network100. Radio frequency (RF) transceiver 410 down-converts the incoming RFsignal to produce an intermediate frequency (IF) or a baseband signal.The IF or baseband signal is sent to receiver (RX) processing circuitry425 that produces a processed baseband signal by filtering, decoding,and/or digitizing the baseband or IF signal. Receiver (RX) processingcircuitry 425 transmits the processed baseband signal to speaker 430(i.e., voice data) or to main processor 440 for further processing(e.g., web browsing).

Transmitter (TX) processing circuitry 415 receives analog or digitalvoice data from microphone 420 or other outgoing baseband data (e.g.,web data, e-mail, interactive video game data) from main processor 440.Transmitter (TX) processing circuitry 415 encodes, multiplexes, and/ordigitizes the outgoing baseband data to produce a processed baseband orIF signal. Radio frequency (RF) transceiver 410 receives the outgoingprocessed baseband or IF signal from transmitter (TX) processingcircuitry 415. Radio frequency (RF) transceiver 410 up-converts thebaseband or IF signal to a radio frequency (RF) signal that istransmitted via antenna 405.

In some embodiments of the present disclosure, main processor 440 is amicroprocessor or microcontroller. Memory 460 is coupled to mainprocessor 440. Memory 460 can be any computer readable medium, forexample, the memory 460 can be any electronic, magnetic,electromagnetic, optical, electro-optical, electro-mechanical, and/orother physical device that can contain, store, communicate, propagate,or transmit a computer program, software, firmware, or data for use bythe microprocessor or other computer-related system or method. Accordingto such embodiments, part of memory 460 comprises a random access memory(RAM) and another part of memory 460 comprises a Flash memory, whichacts as a read-only memory (ROM)

Main processor 440 executes basic operating system (OS) program 461stored in memory 460 in order to control the overall operation ofwireless subscriber station 116. In one such operation, main processor440 controls the reception of forward channel signals and thetransmission of reverse channel signals by radio frequency (RF)transceiver 410, receiver (RX) processing circuitry 425, and transmitter(TX) processing circuitry 415, in accordance with well-known principles.

Main processor 440 is capable of executing other processes and programsresident in memory 460. Main processor 440 can move data into or out ofmemory 460, as required by an executing process. Main processor 440 isalso coupled to I/O interface 445. I/O interface 445 provides mobilestation 116 with the ability to connect to other devices such as laptopcomputers and handheld computers. I/O interface 445 is the communicationpath between these accessories and main controller 440.

Main processor 440 is also coupled to keypad 450 and display unit 455.The operator of SS 116 uses keypad 450 to enter data into SS 116.Display 455 may be a liquid crystal display capable of rendering textand/or at least limited graphics from web sites. Alternate embodimentsmay use other types of displays.

Main processor 440 also is operable to estimate the channel matrix fromthe serving base station (e.g., BS 102). Main processor 440 further isoperable to estimate channel matrices from the strong interfering basestations (e.g., BS 103) when the subscriber station (e.g., SS 116) is inan edge-cell (e.g., the edge of two or more coverage areas 120, 125).

Codebook partitioner 470 is coupled to main processor 440. Codebookpartitioner 470 is configured to divide a codebook into two subsets.Based on the estimated channel matrices, the codebook partitioner 470searches the codebook vector or matrix which maximizes the subscriberstation's own receive signal power, or some other performance measurestogether with the codebook vectors or matrices from the interfering basestations, subject to threshold ε 462. The codebook partitioner 470divides the codebook based on the channel estimations performed by themain processor 440. The codebook partitioner 470 creates a preferred setcorresponding to codebook information, e.g., codebook vectors ormatrices, that will cause an interference in a received signal to beless than or equal to (≦) the threshold ε 462. The codebook partitioner470 also creates a restricted set. The restricted set is the complementof the preferred set. As such, the restricted set corresponds tocodebook information, e.g., codebook vectors or matrices, that willcause the interference in the received signal to be greater than (>) thethreshold ε 462.

In some embodiments, codebook partitioner 470 is a plurality ofinstructions contained within memory 460. In such embodiments, codebookpartitioner 470 is configured to cause the main processor 440 to performthe functions described herein above with respect to the componentcodebook partitioner 470. For example, in such embodiments the mainprocessor 440 divides the codebook into the preferred set and therestricted set.

The threshold ε 462 is a configurable parameter indicating aninterference that SS 116 is able to tolerate. In some embodiments, themain processor 440 is operable to adjust threshold ε 462. The thresholdε 462 is adjusted to increase or decrease an identified number ofcodebook vectors or matrices that will cause an interference in areceived signal to be less than or equal to (≦) the threshold ε 462. Insome embodiments, BS 102, e.g., the serving base station, is operable toadjust threshold ε 462. The threshold ε 462 is adjusted to increase ordecrease an identified number of codebook vectors or matrices that willcause an interference in a received signal to be less than or equal to(≦) the threshold ε 462.

Conventionally, in a so called “closed-loop MIMO system,” a feedbackbased mechanism is used to provide information related to the channelgains from BS 102 (e.g., the serving base station) to SS 116 based onvarious criteria. For example, after performing the channel estimationusing the training signals, SS 116 informs BS 102 which codebook vectoror matrix that maximizes the signal-to-noise ratio (SNR) of the receivedsignal based on the channel from BS 102 to SS 116. SS 116 also includesa value of the expected SNR. Then, BS 102 adapts the format of the databased on the information fed back from the SS 116. BS 102 transmits thedata to SS 116. In this way, the performance (mainly the throughput) ofthe wireless system improves under the standardized codebook constraint.

When the two adjacent subscriber stations (SS 116 and SS 115) arescheduled to receive their data in the same frequency band, inter-cellinterference can occur. The received signals for SS 116 and SS 115 arerepresented by Equation 1:Y ₁ =H ₁₁ X ₁ +H ₂₁ X ₂ +N ₁Y ₂ =H ₁₂ X ₁ +H ₂₂ X ₂ +N ₂,   [Eqn. 1]

For use with Equation 1, N_(T) is the number of transmit antennas at BS102 and BS 103, N_(R) is the number of receive antennas at the userequipments. In Equation 1, H₁₁, H₁₂, H₂₁, and H₂₂ are the respectivechannel gains; where Y_(i) is the N_(R)×1 vector of received signal atsubscriber station i; X_(i) is the N_(T)×1 vector of transmitted signalat base station i; and N_(i) is the N_(R)×1 AWGN noise vector. InEquation 1, SS 116 is denoted as “1” such that Y₁ is the the N_(R)×1vector of received signal at SS 116. Further, SS 115 is denoted as “2”such that Y₂ is the the N_(R)×1 vector of received signal at SS 115.Additionally, BS 102 is denoted as “1” such that X₁ is the N_(T)×1vector of transmitted signal at BS 102. Further, BS 103 is denoted as“2” such that X₂ is the N_(T)×1 vector of transmitted signal at BS 103.

Conventionally subscriber stations only reports to serving base stationsabout the preferred codebook vector or matrix based on the channels fromthe serving base station to the served subscriber station. For example,SS 116 chooses the transmitted codebook vector at BS 102 based on H₁₁and SS 115 chooses the transmitted codebook vector at BS 103 based onH₂₂. By doing this, a strong interference may be created to the receivedsignal at the other subscriber stations from different cells using thesame bandwidth. Especially for the case where the subscriber stationsare cell-edge users, the received power level of the interference signaland that of the intended signal are usually comparable which leads avery low signal-to-interference-and-noise ratio (SINR) at the subscriberstation. In this particular example, the transmitted signal from BS 102to SS 116 (X₁) 140 may cause strong interference for the received signalat SS 115 (X₂) 150 and vice-versa. When either of the subscriberstations in FIGS. 1A and 1B is at a cell-edge, the throughput of thecell-edge subscriber station suffers greatly from the interferencebecause the received power levels of the intended signal andinterference are comparable. This is one of the reasons why the averagecell-edge throughput is significantly lower than the average cellthroughput.

Using Precoding Matrix Indicator (PMI) Restriction, each subscriberstations indirectly feeds back the codebook vector that will cause thehighest interference to the subscriber stations own signal. The codebookvector is fed-back to the interfering base station. Then the interferingbase station excludes the reported codebook vector from the codebook andperforms codebook vector selection on a restricted. In this way, thecell-edge throughput can be improved. However, using this approach, theuser equipment will only report the codebook vector which causes thestrongest interference and even with restrict codebook, the interferencecaused by the interfering base station (interfering eNB) may still bevery high if not the highest.

In some embodiments, the cell-edge throughput is improved bycoordinating between BS 102, BS 103 and SS 116 in a unified way. When SS116 is a cell-edge user, SS 116 may experience a low throughput. The lowthroughput of SS 116 results mainly the interference from BS 103.However, interference avoidance operations, conducted by BS 103, resultin the significant reduction or elimination of the interference. Thiscan be shown as follows for the case where N_(T)=4 and N_(R)=2. Thesingular value decomposition (SVD) of the interfering channel matrix H₂₁is defined by Equation 2:H₂₁=UΛV   [Eqn. 2]

In Equation 2, U is a 2×2 unitary matrix, Λ is a 2×4 matrix, and V is a4×4 unitary matrix. Further, Λ has a structure as defined by Equation 3:

$\begin{matrix}{\Lambda = {\begin{bmatrix}\lambda_{1} & 0 & 0 & 0 \\0 & \lambda_{2} & 0 & 0\end{bmatrix}.}} & \left\lbrack {{Eqn}.\mspace{14mu} 3} \right\rbrack\end{matrix}$

Therefore, as long as the first two elements of VX₂ are zero, there willbe no interference for signal X₁ 140 at SS 116. In other words, as longas N_(T)>N_(R) there are some codebook vectors that can be used by BS103 that will cause little or even no interference for the signal fromBS 102. As such, if SS 116 estimates the channel matrix H₂₁, SS 116 cansend (inform) BS 103 through BS 102 a recommended direction to transmitin terms of little or no interference to the signal between BS 102 andSS 116.

FIGS. 5A and 5B illustrate a codebook partitioner 470 according toembodiments of the present disclosure. The embodiments of the codebookpartitioner 470 shown in FIGS. 5A and 5B are for illustration only.Other embodiments of the codebook partitioner 470 can be used withoutdeparting from the scope of this disclosure.

In some embodiments, illustrated in FIG. 5A, where there is one stronginterference in the received signal, SS 116 can divide the standardizedcodebook into two subsets. The codebook partitioner 470 divides thecodebook by creating a first set 505 (set one) and a second set 510 (settwo) based on the configurable parameter threshold ε 462. Set one 505,also referred to as the preferable set, contains the codebook vectors ormatrices that will cause interference to the receive signals less thanthreshold ε 462. Set two 510, also referred to as the restricted set,contains the complement of the first set 505.

The main processor 440 estimates the channel matrices for BS 103 (e.g.,an interfering base station). The codebook partitioner 470 receives theinterfering channel gain H₂₁. The codebook partitioner 470 appliesEquation 4 to identify codebook information for the preferred set andfor the restricted set.ƒ(H ₂₁ ,P _(i),ε)=VH ₂₁ P _(i)≦ε.   [Eqn. 4]

ƒ(H₂₁,P_(i),ε) is a checking function. The checking function checkswhether the preceding vector P_(i) satisfies a specified criteria. If aP_(i) satisfies the specified criteria, P_(i) is placed in the preferredset S₁ 505. If P_(i) does not satisfy the specified criteria, P_(i) isplaced in the restricted set S₂ 510. Equation 4 illustrates the checkingfunction according to one exemplary criterion. In Equation 4, V is afilter at SS 116.

SS 116 then sends feedback information to BS 103. The feedbackinformation (also referred herein as preceding matrix information) isrelated to the indices of the codebook vectors or matrices of eitherset, or both, depending on predetermined criteria. For example, onecriterion might be the cardinality of the set. That is, SS 116 may useone bit to indicate which set of the indices are chosen, either from thepreferable set or the restricted set.

In some embodiments illustrated in FIG. 5B, where there are severalstrong interferences in the received signal, SS 116 can feedback acombination of the preceding vectors and matrices for each interferingbase station such that a total interference level is less than (<) atolerable threshold ε 462. In such embodiments, the checking function isƒ(H₂₁, . . . H_(K1),{right arrow over (P)}₂, . . . , {right arrow over(P)}_(K),ε). In the checking function, K is the number of base stationsseen by SS 116 such that K-1 is the number of interfering base stations.Further, H₂₁, . . . H_(K1) 515 are the channel matrices from the K-1interfering base stations to SS 116, {right arrow over (P)}₂, . . .,{right arrow over (P)}_(K) are the K-1 codebooks for the K-1interfering base stations, while S_(i) 525 and Ŝ_(i) 530 are thepreferred set and restricted set for an interfering base station “i”.

In one example, SS 116 divides the interference level threshold ε 462into several components. Each of the components corresponds to oneinterference level for one particular interfering base station. In suchexample, the information related to the codebook vectors and matrices isobtained for each interfering base stations using methods as describedabove with respect to FIG. 5A.

At least some of the components in FIGS. 3, 4, 5A and 5B may beimplemented in software while other components may be implemented byconfigurable hardware or a mixture of software and configurablehardware.

FIG. 6 illustrates a time diagram for interference avoidance accordingto embodiments of the present disclosure. The embodiment of the timediagram 600 shown in FIG. 6 is for illustration only. Other embodimentsof the time diagram 600 can be used without departing from the scope ofthis disclosure.

In an example wherein SS 116 and SS 115 are edge-cell subscriberstations located in proximity to each, the communications between SS 115and BS 103 can cause interference in the signals between SS 116 and BS102. Further, the communications between SS 116 and BS 102 can causeinterference in the signals between SS 115 and BS 106.

SS 116 performs channel estimation in step 605. SS 116 performsmeasurements based on reference signals received from BS 102 and from BS103. SS 116 divides the codebook and identifies the preferred set 505and restricted set 510. Thereafter, SS 116 sends feedback information(e.g., a preceding matrix information message) to BS 102 in step 615.The feedback information includes the codebook information such as thepreferred set 505, restricted set 510 or both.

Additionally, SS 115 performs channel estimation in step 610. SS 115performs measurements based on reference signals received from BS 103and from BS 102. SS 115 divides the codebook and identifies thepreferred set 505 and restricted set 510. Thereafter, SS 115 sendsfeedback information to BS 103 in step 620. The feedback informationincludes the codebook information such as the preferred set 505,restricted set 510 or both.

BS 102 and BS 103 exchange information in step 625. BS 102 sends thefeedback information received from SS 116 to BS 103. Additionally, BS103 sends feedback information received from SS 115 to BS 102. Theexchange of information in step 625 may occur simultaneously or atdifferent times such that BS 102 sends sends the feedback informationreceived from SS 116 to BS 103 either before or after BS 103 sends thefeedback information received from SS 115 to BS 102.

In step 635, BS 102 decides the preceding to be utilized in futuretransmissions. BS 102 determines if a codebook vector or matrixidentified within the preferred set from SS 115 can be utilized withoutsignificant impairment to the communications to SS 116. For example, BS102 can determine if an average SNR will pass beyond a base stationthreshold ζ. Thereafter, BS 102 selects a codebook and transmits data toSS 116 in step 645.

In step 640, BS 103 decides the precoding to be utilized in futuretransmissions. BS 103 determines if a codebook vector or matrixidentified within the preferred set from SS 116 can be utilized withoutsignificant impairment to the communications to SS 115. For example, BS103 can determine if an average SNR will pass beyond a base stationthreshold ζ. Thereafter, BS 103 selects a codebook and transmits data toSS 115 in step 650.

In some embodiments, SS 115 sends the feedback information directly toBS 102 in step 660. In such embodiments, BS 103 does not need toexchange information with BS 102 in step 625. BS 102 can use thefeedback information received from SS 115 to decided preceding in step635. However, in such embodiments, BS 102 can still send the feedbackinformation received from SS 116 to BS 103.

It will be understood that illustration of the sequence of theoperations by SS 116 and SS 115 can occur in any order orsimultaneously. For example, the channel estimation performed by SS 115may occur before, after or concurrently with the channel estimationperformed by SS 116. Further, the illustration of the sequence of theoperations by BS 102 and BS 103 can occur in any order orsimultaneously. For example, the decide preceding 640 performed by BS103 may occur before, after or concurrently with the decide precoding635 performed by BS 102.

FIG. 7 illustrates a process for interference avoidance according toembodiments of the present disclosure. The embodiment of theinterference avoidance process 700 shown in FIG. 7 is for illustrationonly. Other embodiments of the interference avoidance process 700 can beused without departing from the scope of this disclosure.

In some embodiments, interfering base stations can avoid interferencewith each other by choosing different codebook vectors within astandardized codebook. This is achieved by allowing the base stations tochoose codebook vectors or matrices to transmit their own signals in thespace which creates little or even no interference to the other cells'subscriber stations in the same bandwidth.

In step 705, SS 116 performs channel estimation. SS 116 maybe, forexample, a cell-edge subscriber station. SS 116 estimates the channelmatrix from BS 102 (e.g., the serving base station). Further, SS 116estimates the channel matrices from BS 103 (e.g., a strong interferingbase station). SS 116 estimates the channel matrices from BS 102 and BS103, respectively, through reference signals.

SS 116 generates feedback information in step 710. SS 116 identifiespreferred codebook vectors or matrices. Based on the estimated channelmatrices, SS 116 searches for a codebook vector or matrix that maximizesa receive signal power for SS 116. Thus, SS 116 generates a precedingvector or matrix for its own serving cell (e.g. from BS 102) to maximizethe received power for SS 116. Additionally, SS 116 can search for acodebook vector or matrix that maximizes some other performancemeasures. SS 116 searches the codebook vector or matrix from BS 102together with the codebook vectors or matrices from BS 103 subject tothe configurable parameter threshold ε 462. Thus, SS 116 identifies orcalculates a number of preceding vectors or matrices such that, whenused by BS 103, an interference in the signal between SS 116 and BS 102will be below threshold ε 462. In some embodiments, SS 116 identifiesonly the codebook vectors or matrices from BS 103 that will cause aninterference in the received signal from BS 102. For example, thecodebook information to each interfering base station can be either thecombination of the precoding vectors or matrices that will createinterference less than or equal to the threshold ε 462 or thecombination of the preceding vectors or matrices that will createinterference greater than the threshold ε 462. In some additional andalternative embodiments, SS 116 divides the standardized codebook into apreferred set 505 and a restricted set 510.

In step 715, SS 116 sends the feedback information (also referred to aspreceding matrix message) to BS 102. The feedback information includescodebook information related to the codebook vectors or matrices. Thefeedback information is reported by SS 16 to BS 102. Additionally,information related to the average SNR (or some other performancemeasures) together with the SNR improvement (or some other performancemeasures) when BS 103 is using the preferred codebook vectors ormatrices are also reported.

For example, for all the channels connected to SS 116, SS 116 sendsfeedback information including codebook information related to eitherthe directions of strong eigen-channels or those of the weakeigen-channels. SS 116 sends this codebook information either to BS 102or to BS 103 directly.

For the system shown in FIGS. 1A and 1B, the interfering channel matrixreceived at SS 116 is H₂₁ 140. SS 116 can send the direction of theeigen-channels of H₂₁ 140 where the corresponding singular value issubstantial. Furthermore, SS 116 may also elect to feedback the receivechannel vector from each antenna to BS 103 directly or indirectlythrough BS 102. For example, for the interfering channel matrix H₂₁ 140,SS 116 can feedback quantized directions of h₁, . . . h_(N) _(R) , whereis defined by Equation 5:H₂₁=[h₁, . . . h_(N) _(R) ]^(T).   [Eqn. 5]

SS 116 may also send, directly to BS 103, the feedback informationrelated to the interfering channel gains with or without the schedulinginformation. For example, SS 116 can send the scheduling information tothe BS 103. Upon receiving the scheduling information, BS 103 may getthe information about interference level and information related to thechannel matrices from previous coordination between BS 103 and SS 116for the particular frequency band.

BS 102 receives the feedback information instep 720. BS 102 processesthe information and identifies that the interfering base station is BS103. Then BS 102 forwards the feedback information to BS 103 in step725.

BS 103 receives the feedback information from BS 102 in step 730. Insome embodiments, BS 103 receives the feedback information directly fromSS 116 in step 730.

In steps 735 and 740, BS 102 and BS 103 respectively select codebookvectors or matrices for future transmissions. In step 740, uponreceiving feedback information from either BS 102 or SS 116, BS 103chooses a codebook vector or matrix to send to SS 115 (.e.g., theintended subscriber station for BS 103). BS 103 can select the codebookvector or matrix to send to SS 115 based on the feedback informationfrom SS 116. BS 102 also chooses a codebook vector or matrix to send toSS 116 in step 735.

For example, BS 103 may choose to restrict the codebook vectors ormatrices, or BS 103 can choose the codebook vectors or matrices from thepreferred set based on the average SNR values of SS 115. To be specific,BS 103 may decide the preceding vectors or matrices to SS 115 dependingon the performance improvement for SS 116 and whether an average SNR forthe communications between BS 103 and SS 115 passes beyond a certainbase station threshold ζ. As another example, if BS 103 identifies thatone or more of the codebook vectors or matrices in the preferred set 505can be used without affecting the SINR of the signal between BS 103 andSS 115, BS 103 may select one of the codebook vectors or matrices in thepreferred set. Additionally, BS 103 may avoid selection of a codebookvector or matrix in the restricted set if the restricted set is thefeedback information that is provided.

In some embodiments, SS 116 sends a special indicator to enable adynamic inter-cell interference coordination. This dynamic overloadindicator is obtained in the “Feedback Information Generating” step 710where either all (or most of) the combinations of the codebook vectorsor matrices will bring an interference level greater than the thresholdε 462 or all the combinations will produce an interference level smallerthan the threshold ε 462. After obtaining this indicator, BS 102 and BS103 can jointly perform inter-cell interference coordination to avoidinter-cell interference.

For example, BS 102 schedules SS 116 to another frequency band (or otherresource blocks) if BS 102 receives the dynamic overload indicator fromSS 116 indicating that all (or most of) the combinations of the codebookvectors or matrices cannot bring the interference level to be smallerthan threshold ε 462.

In some such embodiments, where the SNR between BS 102 and SS 116reaches a predetermined level, SS 116 is configured to raise thethreshold ε 462 such that all the combinations will produce aninterference level smaller than the threshold ε 462. In some additionaland alternative embodiments, where the SNR is above a certain thresholdζ, BS 102 is configured to adjust the threshold ε 462. In suchembodiments, BS 102 can send a separate signal to SS 116 or BS 102 caninclude the adjustment command within existing signaling between BS 102and SS 116.

In an additional example, BS 102 may request that BS 103 not schedulesubscriber stations (e.g., SS 115) in the particular frequency bands(resource blocks) upon receiving the dynamic overload indicator from SS116.

In some such embodiments, SS 116 informs BS 102 that all (or most of)the combinations of the codebook vectors or matrices cannot bring theinterference level to be smaller than threshold ε 462. Thereafter, BS102 utilizes other means, such as, but not limited to, using a differentfrequency band, to transmit to SS 116.

FIG. 8 illustrates another process for interference avoidance accordingto embodiments of the present disclosure. The embodiment of theinterference avoidance process 800 shown in FIG. 8 is for illustrationonly. Other embodiments of the interference avoidance process 800 can beused without departing from the scope of this disclosure.

In some embodiments, interfering base stations can avoid interferencewith each other by choosing different codebook vectors within astandardized codebook. In such embodiments, BS 102 and BS 103 shareinformation related to all the channel matrices. BS 102 and BS 103iteratively find good preceding vectors and matrices that avoidinterference in the others respective signals.

In step 805, SS 116 performs channel estimation. SS 116 maybe, forexample, a cell-edge subscriber station. SS 116 estimates the channelmatrix from BS 102 (e.g., the serving base station). Further, SS 116estimates the channel matrices from BS 103 (e.g., a strong interferingbase station). SS 116 estimates the channel matrices from BS 102 and BS103, respectively, through reference signals.

SS 116 generates channel feedback information in step 810 based on theestimated channel matrices. SS 116 sends, to BS 102, channel feedbackinformation related to the channel matrices to BS 102 and the channelmatrices to BS 103 in step 815. In some embodiments, SS 116 sends thechannel feedback information directly to BS 103 in step 815.

For example, for all the interfering channels connected to SS 116, SS116 sends channel feedback information related to either the directionsof strong eigen-channels or those of the weak eigen-channels of H^(H)H(where H is the interfering channel matrix) The channel feedbackinformation is sent either to BS 102 or to BS 103 directly. For thesystem shown in FIGS. 1A and 1B, the interfering channel matrix receivedat SS 116 is H₂₁. SS 116 can send the direction of the eigen-channels ofH₂₁ ^(H)H₂₁ where the corresponding singular value is substantial.

In some additional embodiments, SS 116 sends quantized information aboutH^(H)H/∥H∥H_(F) ² where ∥H∥_(F) ² is the Frobenius norm of matrix H. Forexample, a different codebook of H^(H)H/∥H∥_(F) ² can be designed forsending the channel feedback information related to the interferingchannel matrix.

BS 102 receives and process the channel feedback information receivedfrom SS 116 in step 820. BS 102 processes the channel feedbackinformation and identifies that the interfering base station is BS 103.Then BS 102 forwards the channel feedback information related to all thechannel matrices obtained from SS 116 to BS 103 in step 825.

BS 103 receives the channel feedback information from BS 102 in step830. In some embodiments, BS 103 receives the channel feedbackinformation directly from SS 116 in step 830.

In steps 835, BS 102 and BS 103 respectively iteratively select codebookvectors or matrices for future transmissions. BS 103 and BS 102iteratively select codebook vectors or matrices for future transmissionsindependent of each other. Upon receiving information from either BS 102or SS 116, BS 103 chooses a codebook vector or matrix to send to SS 115(e.g., the intended subscriber station for BS 103). BS 102 also choosesa codebook vector or matrix to send to SS 116.

FIG. 9 illustrates a process for codebook selection according toembodiments of the present disclosure. The embodiment of the codebookselection process 900 shown in FIG. 9 is for illustration only. Otherembodiments of the codebook selection process 900 can be used withoutdeparting from the scope of this disclosure.

The codebook selection process step 835 for BS 102 is detailed in FIG.9. BS 102 and BS 103 each apply an iterative method to find the codebookvector or matrix. Without loss of generality, the procedures performedat BS 102 are illustrated. However, it will be understood that theprocedures outlined for BS 102 apply equally to BS 103. In suchembodiments, the preceding vector or matrix of BS 102 depends on thepreceding vector or matrix of BS 103 (since it will determine theinterference caused to SS 116).

In step 905, an algorithm is initialized. BS 102 computes a possiblepreceding vector or matrix for BS 103 (let P₂ be the precoding vector ormatrix). Also, BS 102 searches the preceding vector or matrix tomaximize (or minimize) some performance measures based on the assumptionthat BS 103 is using P₂ (let P₁ be the resulting preceding vector ormatrix). For example, BS 102 can search the preceding vector or matrixwhich maximizes the SNR or throughput.

In step 910, BS 102 computes a preceding vector and matrix for BS 103 tomaximize or minimize some performance measures based on the fact that BS102 is using P₁ (update the resulting vector or matrix to P₂). BS 102further updates its preceding vector or matrix under some performancemeasures based on the assumption that BS 103 is using P₂ (update theresulting vector or matrix to P₁).

In step 915, BS 102 determines if P₁ and P₂ are stable such that asteady state has been achieved. If P₁ and P₂ are not stable, then BS 102returns to step 910. If P₁ and P₂ are stable (no change or minimalchange), then BS 102 uses P₁ as the precoding vector or matrix. Asimilar procedure will take place in BS 103 to find P₂.

FIG. 10 illustrates a process for interference avoidance according toembodiments of the present disclosure. The embodiment of theinterference avoidance process 1000 shown in FIG. 10 is for illustrationonly. Other embodiments of the interference avoidance process 1000 canbe used without departing from the scope of this disclosure.

In some embodiments, SS 116 sends an interference avoidance message toBS 102. In such embodiments, the interference avoidance message (IAM) isa value that represents the codebook information, e.g., representseither the preferred set or restricted set of the codebook, or both. Forexample, the IAM may be a single PMI vector and a variable. In response,BS 103 calculates the preferred set based on the single PMI vector andvariable.

In step 1005, SS 116 performs channel estimation. SS 116 maybe, forexample, a cell-edge subscriber station. SS 116 estimates the channelmatrix from BS 102 (e.g., the serving base station). Further, SS 116estimates the channel matrices from BS 103 (e.g., a strong interferingbase station). SS 116 estimates the channel matrices from BS 102 and BS103, respectively, through reference signals.

Then, BS 102 sends a configuration message to SS 116 in step 1010. Theconfiguration message includes the threshold ε 462. In some embodiments,the configuration message contains commands for SS 116 to adjust thethreshold ε 462. Threshold ε 462 indicates the interference level at SS116. In some embodiments, the threshold ε 462 may represent a targetinterference level (e.g., tolerable interference level) for SS 116.Receiving the threshold ε 462 by SS 116 triggers precoding vector ormatrix reporting for inter-cell interference avoidance (or mitigation).

In step 1015, SS 116 performs feedback information generation. SS 116identifies preferred codebook vectors or matrices. Based on theestimated channel matrices, SS 116 searches for a codebook vector ormatrix that maximizes a receive signal power for SS 116. Additionally,SS 116 can search for a codebook vector or matrix that maximizes someother performance measures. SS 116 searches the codebook vector ormatrix from BS 102 together with the codebook vectors or matrices fromBS 103 subject to the configurable parameter threshold ε 462. In someembodiments, SS 116 identifies only the codebook vectors or matricesfrom BS 103 that will cause an interference in the received signal fromBS 102. For example, the codebook information to each interfering basestation can be either the combination of the preceding vectors ormatrices that will create interference less than or equal to thethreshold ε 462 or the combination of the preceding vectors or matricesthat will create interference greater than the threshold ε 462. In someadditional and alternative embodiments, SS 116 divides the standardizedcodebook into a preferred set 505 and a restricted set 510. From theinterference level parameter (i.e., threshold ε 462) obtained from BS102, SS 116 also computes the IAM. The IAM indicates the set ofrecommended or restricted preceding vectors or matrices for theinterfering base stations (e.g., BS 103).

In some embodiments, BS 102 and SS 116 negotiate to feedback thecombination of the preceding vectors or matrices that will createinterference less than or equal to threshold ε 462. Additionally, if SS116 cannot find any combination of the preceding vectors or matricesthat will create interference less than or equal to threshold ε 462, SS116 can feedback codebook vector or matrix only for BS 102.

In additional and alternative embodiments, BS 102 and SS 116 negotiateto feedback the combination of the preceding vectors or matrices thatwill create interference greater than threshold ε 462. Additionally, ifSS 116 cannot find any combination of the precoding vectors or matricesthat will create interference greater than threshold ε 462, SS 116 canfeedback codebook vector or matrix only for BS 102.

SS 116 sends feedback information to BS 102 in step 1020. The feedbackinformation that SS 116 sends includes several elements. In someembodiments, the feedback information includes one or more of:

1. Codebook information, e.g., information related to the codebookvector or matrix which maximizes the receive signal power (or some otherperformance measures) for BS 102 (e.g., the serving base station) andthe information related to the codebook vector or matrix which maximizesthe receive signal power (or some other performance measures) for BS 103(e.g., the interfering base station).

2. Information related to the averagesignal-to-interference-and-noise-ratio (SINR) improvement or some otherperformance measures. For example, this information can represent theachievable average SINR (or some other performance measures) when BS 102is using the precoding vector or matrix feedback from SS 116.

3. The corresponding IAM for each of the interfering base stations(e.g., for BS 103). The IAM sent by SS 116 was computed by SS 116 instep 1015 using threshold ε 462.

In some embodiments, the information related to the average SINRimprovement is a change in channel quality information (ΔCQI) when BS103 is using the recommended set of preceding vectors or matrices.

For example, ΔCQI can be the difference between the expected SINR whenBS 103 is using the recommended set and an expected SINR when BS 103 isnot using the recommended set.

In another example, ΔCQI can be the difference between the worst caseSINR when BS 103 is using the recommended sets and the worst case SINRwhen BS 103 is not using the recommended sets.

In yet another example, ΔCQI can be the difference between the worstcase SINR when BS 103 is using the recommended sets and the expectedSINR when BS 103 is not using the recommended sets

In still another example, ΔCQI can be the difference between theexpected SINR when BS 103 is using the recommended sets and the worstcase SINR when BS 103 is not using the recommended sets.

In some embodiments, SS 116 sends the feedback information directly toBS 103. In such embodiments, SS 116 sends one or more of the codebookinformation related to codebook vector or matrices for the interferencechannel, the IAM message indicating the set of recommended (e.g.,preferred) or restricted preceding vectors or matrices, and theinformation related to SINR improvement if the set is applied at BS 103.

BS 102 receives the feedback information in step 1025. BS 102 processesthe information and identifies that the interfering base station is BS103. Then BS 102 forwards the feedback information to BS 103 in step1030. The IAM indicating the recommended (preferred) or the restrictedset of the precoding vectors or matrices are reported to BS 103. Thecorresponding IAMs for different base stations and the SINR (or otherperformance measures) improvements are forwarded to their respectivebase stations as well.

BS 103 receives the feedback information from BS 102 in step 1035. Insome embodiments, BS 103 receives the feedback information directly fromSS 116 in step 1035.

In steps 1040 and 1045, BS 102 and BS 103 respectively select codebookvectors or matrices for future transmissions. In step 1045, uponreceiving information from either BS 102 or SS 116, BS 103 chooses acodebook vector or matrix to send to SS 115 (.e.g., the intendedsubscriber station for BS 103) based on the feedback information (e.g.,one or more of the preceding codebook vector or matrix, the IAM, and theSINR improvement ΔCQI).

BS 102 also chooses a codebook vector or matrix to send to SS 116 instep 1040. BS 102 may choose a codebook vector or matrix to send to SS116 based on the feedback information (e.g., one or more of thepreceding codebook vector or matrix, the IAM, and the SINR improvementΔCQI) received from another base station or subscriber station.

In some embodiments, when BS 103 receives a request from BS 102, BS 103chooses to follow the recommendation based the SINR improvement report.Once BS 103 decides to follow the recommendation, BS 103 may choose apreceding codebook vector or matrix among the set specified by the IAM.In some such embodiments, BS 103 chooses the preceding codebook vectoror matrix which maximizes the SINR (or other performance measures) fromBS 103 to SS 115 within the set.

In some embodiments, when BS 103 receives multiple requests fromdifferent base stations, BS 103 may choose to follow a recommendationbased on the SINR improvement reports from various base stations. A rankof the requests can be ordered based on ΔCQI and the channel between BS103 and SS 115.

In some embodiments, BS 102 sends an activation message indicating whichsubscriber stations are allowed to participate in the interferenceavoidance process. In such embodiments, BS 102 sends the activationmessage to SS 116 indicating that SS 116 is to report feedbackinformation (e.g., reporting the preferred set or restricted set orsending the IAM). In some embodiments, BS 102 sends the activationmessage to subscriber stations, such as SS 114, indicating that thoserespective subscriber stations will not participate in interferenceavoidance. SS 114 may or may not be an edge-cell device.

In some embodiments, by default all subscriber stations participate inthe interference avoidance process and report feedback information. Insuch embodiments, BS 102 sends a deactivation message to subscriberstations that are not to participate in the interference avoidanceprocess.

In some embodiments, the IAM includes a distance measurement. In suchembodiments, SS 116 generates the IAM based on a distance measure thatpartitions the preceding codebook vectors into two parts. Part one(preferable set S₁ 505) contains the codebook vectors or matrices thatwill cause interference to the receive signals less than threshold ε462; while part two (restricted set S₂ 510) contains the complement ofthe first set. The IAM is actually a threshold to distinguish these twosets under different distance measures. The codebook partitioner 470applies Equation 4 to identify codebook information for the preferredset and for the restricted set.

Again, ƒ(H₂₁,P_(i),ε) is a checking function. The checking functionchecks whether the preceding vector P_(i) satisfies a specifiedcriteria. If a P_(i) satisfies the specified criteria, P_(i) is placedin the preferred set S₁ 505. If P_(i) does not satisfy the specifiedcriteria, P_(i) is placed in the restricted set S₂ 510. Equation 4illustrates the checking function according to one exemplary criterion.In Equation 4, V is a filter at SS 116.

Once the two sets are formed, the codebook partitioner 470 computes thedistance from the elements in one particular set to the precedingcodebook vector or matrix that maximizes the interference power (orother performance measure) received at SS 116. An IAM threshold δ canthen be used to distinguish these two sets.

For example, a chordal distance can be used to measure the distancebetween different preceding codebook matrices and set the threshold tobe the maximum distance from the elements of preferred set to theprecoding matrix which maximizes the interference power.

In some embodiments, BS 102 configures the target tolerable interferencelevel threshold ε 462 and a target SINR improvement ΔCQI. BS 102 sendsthe target tolerable interference level threshold ε 462 and a targetSINR improvement ΔCQI to SS 116 in the configuration message discussedhereinabove with respect to FIG. 10, step 1010. Then, SS 116 performsfeedback information generation (discussed hereinabove with respect toFIG. 10, step 1015). In such embodiments, SS 116 reports the feedbackinformation only if the SINR improvement ΔCQI is greater than the targetSINR improvement ΔCQI. If SS 116 calculates that the SINR improvementΔCQI is not greater than the target SINR improvement ΔCQI, then SS 116does not send the feedback information to BS 102 or BS 103. In some suchembodiments, if SS 116 calculates that the SINR improvement ΔCQI is notgreater than the target SINR improvement ΔCQI, then SS 116 sends amessage to BS 102 indicating that SS 116 cannot meet the target SINRimprovement ΔCQI. Accordingly, based on the feedback information relatedto the average SINR for SS 116, BS 102 may decide to choose differentstrategies to serve SS 116. For example, when the average SINR (or someother performance measures) is large for SS 116, BS 102 may choose notto do anything. When the average SINR (or some other performancemeasures) is small for SS 116, BS 102 may choose to reschedule SS 116 ondifferent resource blocks.

In some embodiments, SS 116 configures the target tolerable interferencelevel threshold ε 462 and a target SINR improvement ΔCQI. In suchembodiments, BS 102 sends the activation message, discussed hereinabove,to SS 116 in step 1010. Then, SS 116 performs feedback informationgeneration (discussed hereinabove with respect to FIG. 10, step 1015).SS 116 configures the IAM threshold δ locally to be sent to BS 103. Forexample, IAM threshold δ is computed based on the locally configuredtolerable interference level threshold ε 462 through different distancemeasures. In such embodiments, SS 116 includes a locally configurabletarget tolerable interference level threshold ε 462. After estimatingthe channels to BS 103 (e.g., the interfering base stations), SS 116 canpartition the precoding codebook vectors and matrices into two sets 505,510 and compute the IAM threshold δ based on different distancemeasures. The examples of the distance measures can be thecross-correlation between different precoding codebook vectors and thechordal distance between different precoding codebook matrices.

In some embodiments, serving base stations configure the targettolerable interference level threshold ε 462 and a target SINRimprovement ΔCQI for participating subscriber stations. In suchembodiments, BS 102 sends the configuration message and activationmessage as unified message to SS 116. Then, SS 116 performs feedbackinformation generation (discussed hereinabove with respect to FIG. 10,step 1015). SS 116 configures the IAM threshold δ locally to be sent toBS 103. SS 116 reports the feedback information only if the SINRimprovement ΔCQI is greater than the target SINR improvement ΔCQI. If SS116 calculates that the SINR improvement ΔCQI is not greater than thetarget SINR improvement ΔCQI, then SS 116 does not send the feedbackinformation to BS 102 or BS 103. In some such embodiments, if SS 116calculates that the SINR improvement ΔCQI is not greater than the targetSINR improvement ΔCQI, then SS 116 sends a message to BS 102 indicatingthat SS 116 cannot meet the target SINR improvement ΔCQI. Accordingly,based on the feedback information related to the average SINR for SS116, BS 102 may decide to choose different strategies to serve SS 116.

For example, when the average SINR (or some other performance measures)is large for SS 116, BS 102 may choose not to do anything.

When the average SINR (or some other performance measures) is small forSS 116, BS 102 may choose to reschedule SS 116 on different resourceblocks.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

1. For use in a wireless communication network, a subscriber stationcapable of performing channel estimation, said subscriber stationcomprising: a processor; a memory; and a codebook partitioner configuredto divide a codebook into two sets, wherein a first set of said two setscorresponds to codebook information that will cause an interference in areceived signal to be less than a threshold and said processorconfigured to send at least one of said two sets to a base station,wherein said threshold is configurable by one of said subscriber stationand a serving base station.
 2. The subscriber station as set forth inclaim 1, wherein said codebook information comprises at least one ofcodebook vectors and codebook matrices.
 3. The subscriber station as setforth in claim 1, wherein said base station is an interfering basestation.
 4. The subscriber station as set forth in claim 3, wherein saidprocessor further is configured to transmit scheduling information tosaid interfering base station.
 5. The subscriber station as set forth inclaim 1, wherein said processor is configured to send a second set ofsaid two sets, said second set corresponding to codebook informationthat will cause an interference in a received signal to be greater thana threshold.
 6. The subscriber station as set forth in claim 1, whereinsaid processor is configured to send an indicator identifying one of arecommended precoding matrix information and a restricted precodingmatrix information.
 7. The subscriber station as set forth in claim 1,wherein the base station is configured to choose a precoding matrix inresponse to the at least one of the two sets.
 8. The subscriber stationas set forth in claim 1, wherein said processor is configured to send anoverload indicator when all of said codebook information will cause aninterference in a received signal to be greater than a threshold.
 9. Thesubscriber station as set forth in claim 1, wherein said processorfurther is configured to transmit a statistical computationcorresponding to a serving channel and one or more interfering channels.10. The subscriber station as set forth in claim 9, wherein saidstatistical computation is related to at least one of a direction of astrong eigen-channel and a weak eigen-channel.
 11. A wirelesscommunications network comprising a plurality of base stations, each oneof said base stations capable of selecting one of a plurality ofcodebooks for precoding, each of said base stations comprising: areceiver configured to receive feedback information from at least onesubscriber station, the feedback information comprising at least one ofa recommended set of codebook information and a restricted set ofcodebook information; and a controller configured to identify the atleast one of the recommended set of codebook information and therestricted set of codebook information, wherein each of the basestations is configured to compute a precoding matrix independently anditeratively.
 12. The network of claim 11, wherein said controller isconfigured to choose the precoding matrix in response to saidrecommended set of codebook information.
 13. The network of claim 12,wherein said controller is configured to choose the precoding matrixthat maximizes its own channel performance measure.
 14. The network ofclaim 13, wherein the controller is configured to choose the precodingmatrix by one of: a cross-correlation method; and selecting from aprecoding matrix closest to its own subscriber station precoding matrix.15. The network of claim 11, wherein said controller is configured tochoose a compliment precoding matrix in response to said restricted setof codebook information.
 16. The network of claim 11, wherein saidcontroller is configured to ignore said feedback information.
 17. Thenetwork of claim 11, wherein said feedback information further comprisesan overload indicator when all of a codebook information will cause aninterference in a signal received by a subscriber station to be greaterthan a threshold.
 18. The network of claim 17, wherein said controlleris configured to schedule said subscriber station to another frequencyband when the feedback information comprises the overload indicator. 19.The network of claim 17, wherein said base station is configured to senda request to an interfering base station to schedule a subscriberstation served by said interfering base station to another frequencyband when the feedback information comprises the overload indicator. 20.The network of claim 17, wherein the threshold is configurable by one ofthe subscriber station.
 21. The network of claim 11, wherein each ofsaid base stations is configured to continue iterative computations,verifying after each iteration, until a steady state of the computedprecoding matrix is obtained.
 22. For use in a wireless communicationnetwork, a method of interference avoidance, the method comprising:receiving configuration information for a threshold: estimating channelinformation; identifying codebook information that will cause aninterference in a received signal to be less than the threshold;dividing a codebook into subsets, wherein at least one subsetcorresponds to the identified codebook information; and transmittingfeedback information associated with the at least one subset.
 23. Themethod as set forth in claim 22, further comprising computing a valuefor the codebook information, the value indicating at least one of a setof preferred precoding vectors, a set of restricted precoding vectors, aset of preferred precoding matrices, and a set of restricted precodingmatrices for an interfering base station.
 24. The method as set forth inclaim 22, wherein transmitting comprises transmitting the feedbackinformation to a serving base station.
 25. The method as set forth inclaim 22, wherein transmitting comprises transmitting the feedbackinformation to an interfering base station.
 26. The method as set forthin claim 22, wherein the feedback information comprises a dynamicindicator indicating that all of said codebook information will cause aninterference in a received signal to be greater than the threshold. 27.For use in a wireless communication network, a method of interferenceavoidance, the method comprising: receiving feedback information, thefeedback information including a set of codebook information thatidentifies one of a recommended set and a restricted set; determining aresponse to said feedback information; selecting a precoding matrixbased on the determined response; and forwarding the feedbackinformation to an interfering base station.
 28. The method as set forthin claim 27, wherein the feedback information further comprises a valuefor the codebook information, the value indicating at least one of a setof preferred precoding vectors, a set of restricted precoding vectors, aset of preferred precoding matrices, and a set of restricted precodingmatrices for an interfering base station.
 29. The method as set forth inclaim 27, further comprising transmitting configuration information fora threshold used to determine said feedback information.
 30. The methodas set forth in claim 27, further comprising selecting a complimentprecoding matrix based on the feedback information.
 31. The method asset forth in claim 27, wherein the feedback information comprises adynamic indicator indicating that all of said codebook information willcause an interference in a received signal to be greater than athreshold.
 32. The method as set forth in claim 27, further comprisingiteratively computing the precoding matrix independently.
 33. The methodas set forth in claim 32, wherein computing further comprises:continuing iterative computations; and verifying after each iterationuntil a steady state of the computed precoding matrix is obtained.